Anyway I have a theory - as does everyone when it comes to this film: Deckard was one of the original escapees and was reprogrammed to hunt down his old friends. Either that or he is a Nexus 7 prototype, like Rachael. He was implanted with Gaff's memories, as Gaff is the original Blade Runner.
I'm sure this isn't a revelation to anyone, and my conclusions are highly debatable, so here's an article by someone who sees things the same way.

(Jump to the "Who was Deckard?" subheading for the juicy stuff)

I had never noticed that Deck's car has clipped wings (incapable of flight), and that he had to be driven around by Gaff any time flying around was necessary. His superiors certainly seem to have quite a leash on him, regardless of whether or not he truly is a replicant.

Deckard is a replicant. Even before it was confirmed by Scott it was pretty clear from the way his eyes reflected the same way and the way Bryant looks at him during the briefing and other signs such as Gaff making the Unicorn origami.

The final cut is the best version of the film and corrected the only real problem I had which was the line "I want more life, fucker". In a way that line works because it shows Roy doesn't have any reverence toward Tyrell but tonally it felt out of place and somewhat jarring.

January Jones is still a total void, code names in a movie setting still sound retarded and Magneto and the Prof needed to be friends for *far* longer to believably be hetero-life partners torn asunder.

However, the spy caper bits were great, especially Magneto: Nazi Hunter. I could have watched an entire movie about that.

All in all, its one of the better superhero movies and its a shame the format didnt gain more ground and allow them to make a proper sequel, rather than smashing the two movie series together.

Far better than the second film and up there with the first, Stark wasn't half as grating in this, they really balanced it well and I enjoyed all the characters who seemed a bit more normal and interesting than usual. Had no idea with the twist which was amusing. Got a bit tiresome towards the end and fell into the CGI grinder like most Marvel films.